Icy Moons Are Ocean Worlds
mceglowski.substack.com
mceglowski.substack.com
Europa Clipper, launched 2024, starts Europa flybys on March 2031
Dragonfly, hopefully launching July 2028, arriving on Titan 2034
> Enceladus is far smaller than the Jovian ocean worlds, roughly the size of Ohio
Why not just say 'has a diameter of about 500 km'? The propensity of astronomers to compare diameters of a small spherical object to a surface patch of a much larger spherical object is intriguing. Similar things happen with 'the Great Red Spot is about two Earths wide'.
If the article said "500km", someone in the comments would go "that's about as wide as Germany!" or similar.
And, since it was km -> "state size", it was almost certainly for the American audience, since they would have used something like the size of Germany for a European, or "twice the size of South Korea" or something.
You said these comparisons are made to make things real or relatable; I personally would expect more out of my audience and give them the magnitude and units directly. I'm not writing for a tabloid; having a strong grounding in units understanding without needing to relate to daily phenomena is in my view critical to not making apparently trivial mistakes that can potentially lead to horrible disasters.
Although, as it turns out, "orbiter" was a poor choice of name.
This is moderately misleading in some ways, but illustrative enough and also technically valid if somebody wants to model it accurately.
I think that this is more than moderately misleading, because it is ambiguous:
- if they meant "diameter is similar to Ohio dimensions", they are a little bit off, because Ohio is about 355*355 km and Enceladus diameter is around 500km
- if they meant surface area, then they are very off, because Ohio is 116,096 km^2 while Enceladus is about 800,000 km^2. In this case it would be more accurate to say that it is bigger then Texas, but smaller than Alaska (if we want to use US states for comparison)
I think they used the diagonal of a hypothetical square Ohio: sqrt(355^2 + 355^2) ≈ 502 km.
"Ohio isn't actually square, though you wouldn't know that from talking to the inhabitants" or some such.
(It is still misleading to compare it to the diameter of an almost-spherical object, I agree. Especially because moving on the surface of a sphere it takes much longer than 502 km to walk from one point to the antipodal one.)
I don't have a concrete proof, just a gut feeling, but I think that this kind of comparisons are much more common in texts written by Americans and for Americans than in any other culture, that's why:
> There's a meme about "Americans will use anything but the metric system" when describing buildings as "100 school buses back to back" or "3 football fields"
Those filthy new worlders and their propensity to make technical writing parsable by the unwashed masses. If the masses want to understand science they should just go to Oxford or whatever.
> make technical writing parsable by the unwashed masses
> If the masses want to understand science they should just go to Oxford
This is a bad strawman. I learnt scientific notation in secondary school. I expect most educated people to understand what is meant by '1.5 × 10^8 km' in an instant. If they don't, then honestly, skill issue, and it is a big indictment of their parent country's education system.
> But it is a much more exciting place than Ohio, and far more livable.
Maybe just an excuse to make a joke about Ohio.
What would size here refer to surface area? Or diameter? Or circumfence?
Seems odd to neglect to mention New Horizons immediately after mentioning the probable existence of liquid oceans under Pluto's surface, a finding made possible thanks primarily to New Horizons.
It was a valuable piece of corroborating evidence, but not shocking and unexpected in the way results from those three missions were. We had good reason to believe Pluto would look a lot like Triton, and it does.
If there are planetologists reading the thread, I'd love to hear a more authorative perspective than mine!
> We want rocks in contact with water,
But there is ice compressed between the water column and the xenoceanic bottom, ok. I see the problem.
What about rocks in the surface of the water?. Some volcanic rocks can float.
This is... not something you lay plans on. Even on Earth, these rocks are formed at surface pressure, just barely float, and don't float for long (I've tried). If they form in the deep ocean, I'm guessing the pressure isn't going to let the bubbles be big enough to create bouyancy at all. Either way they would be super rare.
1) Animals can synthesize "rocks" with hard materials that will sink naturally, but that are buoyant while their owners are alive. This means that we can expect a thin layer of a fake "rocky" bottom in form of Thanatocenose just in the surface of the second layer of ice. Bony or Shelly bottom would be a better way to define it.
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2) If those hypothetical mineral resources are rare, organisms would be hard pressed by evolution to start collecting them.
Some animals collect pebbles to make pods. If the upper ice layer was created after the lower ice layer we may find aliens dressed on a meteorite's cape. This meteorites don't necessarily need to sink if included in the body of an organism. The Earth developed similar solutions that can be colonial, like Sabellaria worms, or individual, like caddisfly larvae.
Fill this pods with organisms able to extract the energy of chemical links in those rocks, and you have food and refuge in the same packet. Go a little further and you developed luminescence. We can't guarantee that this life evolved eyes, but bioluminescence is the most popular way to communicate among life beings on earth so if aliens didn't evolved eyes the alternative solutions will became very bizarre and unexpected really fast.
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3) Maybe we will not need to dig all the way down to find life. Biocenosis will fit every possible niche, so is 100% guaranteed that the transition "upper ice layer" -> "liquid surface" will be colonized by life.
First because it poses a topological advantage (halves the directions of possible attacks by predators, and allows predators to ambush and hide in irregular ice).
Evolution later would select organisms that burrow up in the ice layer. Burrows are a safer place to rest and nest than just a surface of ice, so the trait would be selected fast by evolutionary pressure. We can expect tunnels shaped as and 'A' populated by filterers also. They will create currents between an entry and an exit to use the energy more efficiently
So we may suspect the presence of life if we can detect indirectly a thin layer in the ice/water frontier that: a) is less dense than ice, but more dense than liquid or gas bubbles, and b) is structurally different than what physics would predict for the formation and extension of ice cracks.
And if there aren't any alterations in this boundary, it may be no life at all, or life may be very rare.
> The radiation environment around Europa is punishing; an astronaut standing on the surface would get a fatal dose in about a day
Io, meanwhile, is 35 Sv/day. Location really matters among the four Galilean moons.
Jupiter and Io have a very interesting symbiosis. Jupiter melts Io to form dusty volcanos. It then magnetically sweeps Io clean of dust. The dust forms a plasma ring that enhances the same magnetic field.
Iceans may be confusing, as it does not suggest a liquid stage under the platform, and ice suggests presence of water in something that is not necessarily composed of water, but the second layer of ice created by pressure is something never found before for sure, so it may deserve a chance.
Very cool worlds. Finding an entire alien marine ecosystem would be incredible.
> The radiation environment around Europa is punishing; an astronaut standing on the surface would get a fatal dose in about a day
This is disappointing to hear because I'd always imagined Europa as the next destination after Mars. Radiation also affects electronics so even a robot couldn't be a permanent visitor.